1. Field of the Invention
The present invention relates to bonded abrasive articles comprising silane coupling agent treated abrasive particles dispersed throughout and adhered within polyurethane binders.
2. Description of Related Art
Abrasive products formed of a solid or foamed organic polymeric matrix having abrasive granules dispersed throughout and bonded therein are widely used and are known as "bonded" or "molded" abrasives. Typically, the polymeric matrix is composed of either a hard thermoset resin, such as base-catalyzed phenol formaldehyde, or a resilient elastomeric resin, such as a polyurethane or a compounded rubber composition.
The hard thermosetting resins generally have a high tensile strength and a low elongation at failure, and produce bonded abrasive products which are resistant to significant change when subject to elevated temperatures. However, these hard thermoset resin bonded abrasive products are susceptible to brittle fracture and have the disadvantage of leaving "chatter" marks on the workpiece, particularly when used in off-hand operations.
The elastomeric resins generally produce an abrasive product having some degree of flexibility and resiliency. Typically, these articles provide a smoother abrasive action and a finer surface finish than a hard thermoset resin bonded article. Because of this, flexible elastomeric resin bonded abrasive articles have found a broad range of industrial applications such as in the metal-working and wood-working industries for deburring, finishing and sanding. Unfortunately, however, these elastomeric resin bonded articles often show significant softening at elevated temperatures as might be encountered when an abrasive product is urged against a workpiece at high surface speeds and/or high pressures. Such softening often results in the premature loss of abrasive particles, the undesirable smearing or transfer of portions of the abrasive article to the surface of the workpiece in the case of metal-working applications, or the glazing over of the article's surface in the case of wood-working applications.
Conventional elastomeric resin bonded abrasive articles typically use an elastomeric polyurethane as the binder matrix. The polyurethane binder matrix may be a foam or a solid. Furthermore, the polyurethane binder matrix may be formed of a linear or crosslinked polymer network.
Attempts to form a resilient yet smear-resistant polyurethane binder by introducing a moderate amount of crosslinking into the polyurethane network with standard crosslinking techniques using polyfunctional isocyanates and polyfunctional polyols have yielded marketable bonded abrasives. However, perhaps due to the extended distances between crosslinks, the amount of crosslinking necessary to provide smear-resistance by these standard crosslinking techniques typically makes the resin hard and brittle, and thus the articles do not have optimum cutting ability.
While the most common application for silane coupling agents is to bond an inorganic substrate to a polymer, the prediction of which silane coupling agent is best for a given inorganic/polymer system is extremely difficult. In the case of abrasive articles, coupling agents which demonstrate improvement in the qualities of increased cut, decreased wear, increased smear-resistance, and resistance to loss of abrasive grains under end-use conditions are most important. The abrasives industry is constantly seeking improved flexible molded abrasive articles that will not smear or glaze when used at high surface speeds and/or high operating pressures and have increased cut with decreased (or no significant increase) in wear.